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Discussion papers
https://doi.org/10.5194/os-2019-28
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-2019-28
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Apr 2019

Research article | 17 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

High-resolution under-water laser spectrometer sensing provides new insights to methane distribution at an Arctic seepage site

Pär Jansson1, Jack Triest2, Roberto Grilli2, Bénédicte Ferré1, Anna Silyakova1, Jürgen Mienert1, and Jérôme Chappellaz2 Pär Jansson et al.
  • 1CAGE Center for Arctic Gas Hydrate, Environment, and Climate, Department of Geosciences, UiT-The Arctic University of Norway, 9037, Tromsø, Norway
  • 2Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, 38000 Grenoble, France

Abstract. Methane (CH4) in marine sediments has the potential to contribute to changes in the ocean- and climate system. Physical and biochemical processes that are difficult to quantify with current standard methods such as acoustic surveys and discrete sampling govern the distribution of dissolved CH4 in oceans and lakes. Detailed observations of aquatic CH4 concentrations are required for a better understanding of CH4 dynamics in the water column, how it can affect lake- and ocean acidification, the chemosynthetic ecosystem, and mixing ratios of atmospheric climate gases. Here we present pioneering high-resolution in-situ measurements of dissolved CH4 throughout the water column over a 400 m deep CH4 seepage area at the continental slope west of Svalbard. A new fast-response under-water membrane-inlet laser spectrometer sensor demonstrates technological advances and breakthroughs for ocean measurements. We reveal decametre-scale variations of dissolved CH4 concentrations over the CH4 seepage zone. Previous studies could not resolve such heterogeneity in the area, assumed smoother distribution and therefore lacked both details and insights to ongoing processes. We show good repeatability of the instrument measurements, which are also in agreement with discrete sampling. New numerical models, based on acoustically evidenced free gas emissions from the seafloor, support the observed heterogeneity and CH4 inventory. We identified sources of CH4, undetectable with echosounder, and rapid diffusion of dissolved CH4 away from the sources. Results from the continuous ocean laser-spectrometer measurements, supported by modelling, improve our understanding of CH4 fluxes and related physical processes over Arctic CH4 degassing regions.

Pär Jansson et al.
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Replication Data for: High-resolution under-water laser spectrometer sensing provides new insights to methane distribution at an Arctic seepage site P. Jansson, J. Triest, R. Grilli, A. Silyakova, J. Mienert, and J. Chappelaz https://doi.org/10.18710/UWP6LL

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Short summary
Methane seepage from the seafloor west of Svalbard was investigated with fast-response membrane inlet laser spectrometer. The acquired data was in good agreement with traditional sparse discrete water sampling, subsequent Gas Chromatography, and with a new 2D model, based on echosounder data. However, the acquired high-resolution data revealed unprecedented details of the methane distribution, which highlights the need for such methods, for future climate studies.
Methane seepage from the seafloor west of Svalbard was investigated with fast-response membrane...
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